The subject invention is generally directed to thermal ink-jet printers, and more particularly to techniques for achieving reliable start up operation of thermal ink-jet pens.
An ink-jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes "dot locations," "dot positions," or "pixels". Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink-jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
An important consideration with thermal ink-jet printers is improper operation due to clogged nozzles, particularly upon start up of a print operation after a printhead has not been used for some time. The presence of clogged nozzles prior to start up of a print operation cannot be visually detected, and thus the presence of clogged nozzles would be manifested by a bad printer output, which is wasteful since the subject matter intended to be printed would have to be printed again and moreover since the clogged nozzles would not necessarily have been cleared prior to the repeat print.